NEW YORK (Reuters
Health) - Even mild physical activity,
such as walking, gardening and working around the house, can help
keep the heart healthy, but such activities do little to make
bones stronger, according to a new study.

"Although some activity may be
better than none at all for certain aspects of health, like heart
health, milder forms of activity may not be sufficient to hold
off or attenuate the age-related decline in bone with aging,"
said lead author Dr. Kerry J. Stewart of Johns Hopkins University
School of Medicine in Baltimore, Maryland. "More vigorous exercise
may be needed," he told Reuters Health.

Although mild activity and aerobic
fitness did not seem to affect bone density in the study, having
greater muscle strength and carrying extra pounds around the middle
were related to stronger bones, according to a report on the findings
that is published in November issue of the Journal of Internal
Medicine.

Despite the apparent link between
abdominal obesity and stronger bones, the study does not give
the green light to pig out, Stewart cautioned.

"Although being fat may be good
for bone density, gaining weight is not the answer because of
the harmful effects of obesity on many other aspects of health,"
he said.

Stewart's team studied 38 men and
46 women who were generally healthy, although their blood pressure
was at the high end of the normal range or mildly high. None of
the participants exercised regularly.

In the study, neither overall aerobic
fitness nor participation in mild physical activity had a significant
effect on bone mineral density. But muscle strength as well as
extra fat in the abdomen were associated with denser bones.

"We found that being more fat and
having stronger muscle, which is common in fatter people, along
with hormone replacement therapy, had the most influence on bone,"
Stewart said. "In particular, having more abdominal fat was most
strongly linked to bone density."

The study did not look at how carrying
around extra pounds may boost bone density, but Stewart suggested
that the hormone leptin may be involved. Leptin levels tend to
be higher in fatter people, he explained, and animal studies have
shown that leptin increases the activity of bone cells.